Conventionally, various controls of a rotary electric motor based on a primary magnetic flux, i.e., so-called primary magnetic flux controls have been proposed. Briefly speaking, the primary magnetic flux control is a technique for stably controlling the rotary electric motor by controlling the primary magnetic flux of the rotary electric motor in accordance with a command value thereof.
It is assumed, for example, that a phase of a field flux Λ0 is employed at a d axis in a rotating coordinate system, a phase of a primary magnetic flux [λ1] (this is treated as a vector having a direction and amplitude) is employed at a δ axis in another rotating coordinate system, and a phase difference of the δ axis with respect to the d axis is a load angle ϕ. It is noted that, herein, a γ axis is employed at a 90-degree leading phase with respect to the δ axis. Further, a δc axis and a γc axis are defined as control axes in the rotating coordinate system which is employed in the control of the primary magnetic flux [λ1]. The δc axis and the γc axis correspond to the δ axis and the γ axis, respectively, and a phase difference of the δc axis with respect to the d axis is assumed as ϕc.
In this case, a command value of the primary magnetic flux [λ1] (hereinafter, referred to as a “primary magnetic flux command value”) [Λ1*] (this is treated as a vector having a direction and amplitude) has a positive value Λδ* as a δc-axis component, and a γc-axis component is zero. Therefore, when the primary magnetic flux [λ1] is coincident with the primary magnetic flux command value [Λ1*], the δc-axis component λ1δc of the primary magnetic flux [λ1] is equal to the positive value Λδ* (this is also the amplitude of the primary magnetic flux command value [Λ1*]), and the phase difference ϕc is equal to the load angle ϕ, and the δc axis is coincident with the δ axis.
In the primary magnetic flux control, control, for example, of a voltage command value to be corrected is performed so that not only the δc-axis component λ1δc of the primary magnetic flux [Λ1] should be made equal to the amplitude Λδ* of the primary magnetic flux command value [Λ1] but also a γc-axis component λ1γc thereof should be zero. The phase difference ϕc is thereby coincident with the load angle ϕ.
In this manner, in the primary magnetic flux control, the amplitude Λδ of the primary magnetic flux [λ1] is made equal to the amplitude Λδ* of the command value [Λ1*], and the phase difference ϕc is made coincident with the load angle ϕ, whereby a torque T of the rotary electric motor can be controlled in proportion to the γc-axis component iγc of the amplitude ia of the armature current independently of a rotation angle velocity. Normally, the control is performed on the assumption that the amplitude Λδ* is constant.
Specifically, a number of pole pairs n, the current amplitude ia, a phase (a so-called current phase) β with respect to a q axis (this is a 90-degree leading phase with respect to the d axis) of the armature current, and the amplitude Λδ are introduced into the following expression (1) to find the torque T.
                                                        T              =                            ⁢                                                n                  ·                                ⩓                                                      δ                    ·                    i                                    ⁢                                                                          ⁢                  γ                                                                                                        =                            ⁢                                                n                  ·                                ⩓                                                      δ                    ·                    i                                    ⁢                                                                          ⁢                                      a                    ·                                          cos                      ⁡                                              (                                                  ϕ                          -                          β                                                )                                                                                                                                                    (        1        )            
Note that, among the following prior-art documents, in Yabe and Sakanobe, “A Sensor-less Drive of IPM Motor with Over-modulation PWM”, The papers of Joint Technical Meeting on Rotating Machinery, IEE Japan, 2001 (159), pp. 7 to 12, the δ axis and the γ axis are exchanged and employed, as compared with those in the following other prior art documents: Japanese Patent No. 3672761; Japanese Patent Application Laid-Open No. 4-91693 (1992); Hotta, Asano, and Tsunehiro, “Method of controlling Position Sensorless DC brushless motor”, 1988 Tokai-Section Joint Conference of the Institutes of Electrical and Related Engineers, p. 161; Kaku and Tsunehiro, “A Novel Technique for a DC Brushless Motor Having No Position-Sensors”, 1990 Tokai-Section Joint Conference of the Institutes of Electrical and Engineers, p. 172; Kaku, Yamamura, and Tsunehiro, “A Novel Technique for a DC Brushless Motor Having No Position-Sensors”, IEEJ Transaction on Industry Applications, 1991, Volume 111, No. 8, pp. 639 to 644; Urita, Tsukamoto, and Tsunehiro, “Constant estimation method for synchronous machines with the primary magnetic flux controlled”, 1998 Tokai-Section Joint Conference of the Institutes of Electrical Engineers, p. 101; Urita, Yamamura, and Tsunehiro, “On General Purpose Inverter for Synchronous Motor Drive”, IEEJ Transaction on Industry Applications, 1999, Volume 119, No. 5, pp. 707 to 712; and Takeda, Matsui, Morimoto, and Honda, “Design and Control of Interior Permanent Magnet Synchronous Motor”, Ohmsha, 2001, pp. 23 to 26.